Legionaries were the soldiers of the Roman Republic and Empire, who collectively formed groups of between 1,000 and 6,000 men called legions. Legionaries are widely regarded as some of the most efficient and effective military personnel of the ancient world. Legionaries achieved astonishing victories over the Greeks, the Carthaginians, and dozens of barbarian tribes, often in the face of far more numerous armies.

Five distinct types of legionaries served in the Roman legions: light infantry, cavalry, and three kinds of heavy infantry. Members of the light infantry, or velites, were armed with a short sword called a gladius, a bundle of light javelins, and a small round shield that offered limited protection.

Velites tended to be recruited from poor citizens who could not afford more elaborate weapons and armor. They were not organized into rigid units; they served instead in a flexible support role to assist the other types of legionaries.

The cavalry, or equites, were the most elite and prestigious unit in a Roman legion and tended to number approximately 300 legionaries, regardless of the size of the rest of the legion. They were armed with a comparatively long sword called a spartha, several javelins, body armor, a helmet, and a round shield.

Most equites were wealthy citizens who could afford the expense of their equipment and horses. Their main role in battle was to charge at enemy soldiers, particularly when the foes were retreating. Many wealthy Roman citizens became equites in order to provide a foundation for later political careers.

Roman heavy cavalry, equites

Heavy infantry tended to be drawn from wealthy citizens and were divided into three classes based on age. The youngest heavy legionaries, those in their late teens and early 20s, formed the hastati, which made up the legion’s front line.

The second line of heavy infantry was made up of men in their late 20s and early 30s, who were known as principes, or men in the "prime of their lives". They were armed with a gladius, two heavy javelins, heavy body armor, and a large semicylindrical shield called the scutum.

Finally, the third line of heavy infantry was made up of older and very experienced legionaries, the triarii. Triarii were generally equipped with the heaviest armor and carried a long and heavy spear instead of javelins. The primary role of all heavy infantry was to directly engage enemy troops and fight to the death.

Centurions fighting alongside the legionaries they commanded

In the fourth and fifth centuries b.c.e. heavy legionaries fought in units called maniples, which were commanded by centurions. The maniples were arranged in a checkerboard formation so that the maniples in the second line, the principes, would cover the gaps in the front line of hastati. Maniples of triarii, in turn, covered the gaps in between the maniples of principes.

When marching across a battlefield to engage their enemies, Roman heavy legionaries would first throw their javelins to disrupt the enemy’s front lines. Following this, they used their shields to protect themselves and punch at their enemies in face-to-face combat while stabbing with their short swords.

Their goal was to open a hole in the enemy front lines, break the enemy formations, and convince the enemy to flee in panic. Velites would assist by throwing more javelins at the enemy to further disrupt their lines. Finally, when the enemy broke, the Roman equites would chase them down and try to inflict additional casualties.

Legionaries marching across a battlefield to engage their enemies

The expense of maintaining a large number of elite soldiers was enormous. As a result, the legionaries disappeared as a class of soldier in the fifth century c.e. when the political and economic infrastructure needed to support them collapsed.